The present invention relates to a preserving solution for blood or packed blood cells (hereinafter generically referred to as "blood", unless otherwise noted) for transfusion and a method for preserving blood by using the preserving solution.
Heretofore, blood for transfusion was taken into a sterilized sealed container in which a preserving solution containing an anticoagulant and glucose was placed and preserved at low temperatures within the range of 4.degree. to 6.degree. C. (5.degree. C. on the average) in a refrigerator.
The most common blood preserving method which was utilized in many countries was a method wherein CPD solution, which had a formula wherein a phosphate was added to ACD solution being an original anticoagulant solution, was used as a preserving solution, and blood mixed with CPD solution was preserved at 4.degree. to 6.degree. C. The reason why this method was widely used was that there were may papers reporting that CPD solution which had the formula wherein a phosphate was added to ACD solution had a stronger buffer effect against pH change due to the presence of the phosphate, as compared to ACD solution which contained citric acid, citrate and glucose, and accordingly the functions of erythrocytes preserved could be maintained at a higher level.
Further, in order to prevent the lowering of the functions of erythrocytes during preservation which could not be prevented by using CPD solution, there was proposed a method using a preserving solution wherein a substance such as inosine, adenine or adenosine was added to CPD solution. Such preserving solutions wherein adenine was added to CPD solution were generally used in the United States of America and other countries. However, it is said that this method is less than perfect, from the standpoint that there is a possibility that a surplus of the additive such as adenine, or hypoxanthine which is a metabolite of the additive causes an adverse effect after the preserved blood is transfused into a human body.
Moreover, cells have Na--K pump by which the concentrations of electrolytes in the inside and outside of each cell are controlled. Hemocytes including erythrocytes also have the Na--K pump. It is well known that when blood is preserved at low temperatures, the function of the pump is lowered, which causes the following phenomena: With respcet to Na.sup.+ which is present in a large quantity in plasma among the electrolytes in blood, the concentration of Na.sup.+ in plasma is gradually lowered during storage. With respect to K.sup.+ which is present in a small quantity in plasma, the concentration of K.sup.+ in plasma is gradually increased due to exudation of K.sup.+ from hemocytes. Further, it is well known that hemolysis occurs with prolonged period of preservation, which results in an increase in the amount of free hemoglobin. The above-mentioned phenomena cause serious clinical problems. Nevertheless, there has not been made any improvement with respect to the phenomena up to date.
With respect to the blood preserving temperature, Parpart reported, in 1947, a study wherein blood was preserved at temperatures over the range of 0.degree. to 15.degree. C. The report described that while preservation at a low temperature was preferable to maintain the function of erythrocytes, preservation at a temperature higher than the preserving temperature (4.degree. to 6.degree. C.) adopted at present was preferable to prevent changes of the concentrations of electrolytes including the decrease in the amount of Na.sup.+ and the increase in the amount of K.sup.+ in plasma, and hemolysis during preservation. The preserving temperature (4.degree. to 6.degree. C.) adopted at present was determined by taking into consideration the knowledges obtained from the report and a fluctuation in the temperature control of a refrigerator at that time, and further from the standpoint of surely avoiding damages resulting from freezing.
However, the manufacturing technique of refrigerators has been greatly advanced since then and the presently available refrigerators have been significantly improved in performance. Uda et al reported that any remarkable hemolysis did not occur even when the preserving temperature was lowered to -1.degree. C. during still longer storage condition for six weeks (at the 33rd Congress of Japan Society of Blood Transfusion, June, 1985, in Sendai, Japan).
Even though the allowable period of preservation can be extended by the method of lowering the preservation temperature so as to slow down the metabolism of erythrocytes, it was found that the above-mentioned decrease in Na.sup.+ concentration and increase in K.sup.+ concentration could not be suppressed. Moreover, it was reported by Nishikawa et al that the low-temperature preservation tended to increase hemolysis as compared to the conventional preservation at 4.degree. to 6.degree. C. (at the 34th Congress of Japan Society of Blood Transfusion, June, 1986, in Nagoya, Japan).
There is a freezing-preservation method wherein erythrocytes are completely frozen as a blood preservation method which has given actual results other than the above-mentioned methods. This method is suitable for a long-term preservation wherein a unit of preservation time is year, because the functions of erythrocytes are not damaged through storage. It is necessary to add large quantities of chemicals such as glycerin to blood as a cryoprotective agent. When the preserved blood is thawed without removing the glycerin added in a large quantity, the blood is readily hemolyzed. Therefore, it is essential to quickly remove cryoprotective agents such as glycerin added in a large amount before transfusion of such frozen and thawed blood. The work requires a great deal of labor and time and also special device and container, which results in increase in cost. Therefore, the freezing method has been used mainly to preserve a rare type of blood and has not spread as a general blood preserving method.
It is an object of the present invention to provide a preserving solution for blood which is capable of suppressing the decrease in Na.sup.+ concentration and the increase in K.sup.+ concentration in plasma and the increase in amount of free hemoglobin caused by hemolysis, whereby a preservation at a temperature lower than the conventional preserving temperature is made possible.
Another object of the present invention is to provide a method for preserving blood whereby the lowering of the functions of erythrocytes are suppressed while reducing hemolysis to a lower level, which enables a prolonged preservation of blood.
These and other objects of the present invention will become apparent from the description hereinafter.